offroad has lower axle ratio (3.36 vs 2.94) (although the lower axle ratio also comes with the Big Tow package), rancho shocks (which are nothing special and probably need to be replaced by now), better skid plates, 17" alloy wheels, and perhaps the e-locker in the rear differential (there will be a switch on the dash to lock the rear axle, if so equipped). The original version of the e-locker was a two spider design and subject to failure. It was improved to a 4-spider design at some point (my best guess is 2007). The 2004-2007 trucks have 32 spline axles and are compatible with the aftermarket TrueTrac LSD, which replaced the oem carrier and failure prone spider gears. To install the TrueTrac in an e-locker rear axle, you also have to replace one axle shaft because the e-locker rear axle uses axle shafts of unequal length. Arb also has a full locker for 2004-2007 trucks.
Both are overpriced IMO. The poster above clearly told you the differences between the two. The offroad has lower gears and a tow package. The offroad also has rancho shocks but that dosen't matter because they need to be replaced by now anyways. If you pull or tow the offroad will be better.
I'd go with the one that has over 2yrs less mileage on the clock (if you only put the norm 10-12k miles per year) out of the two choices. Agree with above...at those miles you should be looking at around 9 - 12 grand max for a 5yr old truck. If they are trade-ins from a dealer, there is no way they gave more than 10 g for 'em.